Optical Pyrometer for Temperature Measurement (Chapter 9) An optical pyrometer is a device used to measure the temperature of high-temperature surfaces. In this instrument, an image of the hot surface is compared to the image of a heated filament whose temperature can be adjusted. When the color of the two images is the same, the unknown surface temperature equals that of the filament. Typically, a calibration table giving filament temperature versus filament-heating current is provided by manufacturers in their sales catalogs. Assuming the filament is contained in an evacuated optical chamber, design the filament and the power supply needed to achieve temperatures from 1000 K to 2500 K. Consider platinum and tungsten as candidate filament materials. Discuss the implication of the filament emissivity and the emissivity of the surface under analysis and how this will affect the accuracy of the measurement. Suggest methods that could be used to automate the device so that it could essentially become an on-line temperature-measurement device.